The present invention relates to a method and device for frequency-modulated continuous-wave radar detection with removal of ambiguity between distance and speed. It can be applied especially to radars for automobiles moving in a multiple-target environment, for example when the targets present are relatively grouped together.
There are known ways of fitting out automobiles with radars for road traffic control. These radars in particular carry out the functions of speed regulation or obstacle detection. A speed regulation radar for automobiles has the function in particular of detecting the distance and speed between a carrier vehicle and the vehicle preceding it, in order to enable the carrier vehicle to adjust its speed with respect to the preceding vehicle, in order to meet, for example, safety criteria. A radar of this kind moves essentially in a multiple-target environment. Furthermore, the targets that are present are relatively grouped together:
either with respect to a certain speed with unspecified distances, especially when the target vehicles follow each other in a traffic queue or when the detected targets actually correspond to ground echoes; PA1 or with respect to a certain distance with various speeds, especially when one vehicle is being overtaken by another. PA1 The sensitivity of the radar is reduced for two main reasons: PA1 There may remain erroneous cases of removal of ambiguity. This actually creates "ghost" blips, all the more so as the frequency resolution is reduced by the distribution of the target observation time.
Since a simple version of a frequency-modulated continuous-wave radar, hereinafter called an FM-CW radar, consists of the linear frequency modulation of the continuous wave on a given waveband, there are known ways, if only one target can be illuminated at a given point in time, of removing the ambiguity between the distance and the speed by alternating frequency modulation ramps with opposite slopes. In certain multiple-target situations, a third frequency ramp is used, generally with a zero slope and then finally a fourth sequence may be necessary to remove the doubt.
This approach has major drawbacks, especially the following:
the target observation time must be divided into three or four intervals of integration; PA2 the target must be detected at each of the sequences.